1. Field of the Invention
The present invention relates generally to a retractable seal double-block and bleed plug valves and more specifically, to a plug therefor which incorporates a boundary layer affecting surface perturbations in selected flow surfaces of the valve plug to create turbulent boundary layer flow which generates a beneficial stabilizing torque tending to reduce or eliminate holding forces conventionally required by mechanical parts such as detent mechanisms.
2. Prior Art
Presently double-block and bleed plug valves throughout the valve industry have their plugs held open by mechanical detents. On lever operated valves the open plug position is maintained by handles which drop into recesses. On hand operated valves the open plug position is maintained by detent plungers dropping into recesses. On gear operated valves the open plug position is maintained by self-locking worm gears. Each of these techniques to keep the valve open is needed in conventional plug-type valves because of the closing torque that is generated by flow through the open plug of the valve. Such a closing torque which is inherent in both flow-through plug-type valves can slam the valve shut causing a dangerous water-hammer effect which can produce piping failures and valve leaks which in some cases can threaten the environment. Thus, it has been necessary in prior art plug-type valves to provide mechanical means for resisting the closing torque resulting from the flow-through plus. However, special detent mechanisms, special worm gears and the like all increase the cost of the valve while at the same time presenting a potential reliability problem because of the mechanical wear on such mechanisms for resisting the closing torque.
Thus it would be a highly advantageous characteristic of plug-type valves if it were possible to provide a configuration which produced a torque responsive to flow in the opening direction counter the normally closing direction torque that is normally produced in conventional plug-type valves by flow through the plug. It will be seen hereinafter that the present invention provides such a counter-effect torque by providing surface perturbations in selected flow surfaces of the valve plug to create turbulent boundary layer flow along such surfaces. Such turbulent boundary layer flow generates a beneficial stabilizing torque which by appropriate selection of the surfaces on which the perturbations are provided can be in a direction opposite the closing torque normally incurred in a plug-type valve of the prior art. A search of the prior art has failed to disclose any patents which describe the use of such turbulent boundary layer flow perturbations in a plug-type valve to solve the problem described herein. More specifically, the following U.S. patents were found in a search directed to the present invention, U.S. Pat. Nos.
3,430,919 Frazier PA0 3,591,129 Hulsey PA0 3,689,026 Self PA0 3,814,378 Wurzburger PA0 3,826,281 Clark PA0 4,103,868 Thompson PA0 4,135,544 MacLeod PA0 4,623,119 Van der Wiel PA0 4,982,928 Avelov PA0 5,011,115 Smith et al PA0 5,018,703 Goode
Of the aforementioned patents the following are deemed to be the most relevant to the present invention:
U.S. Pat. No. 4,103,868 to Thompson is directed to a ball valve having an improved ball element design with a plurality of reaction faces which, when contacted by liquid flow through the valve, serve to generally counterbalance the normal self-closing forces exerted upon the ball element by the liquid flow. The ball valve with housing and chamber, has a ball element rotatably supported with a passage positioned so as to be alignable with an inlet and outlet. The passage is defined by edge portions at the outer surface of the ball element. Each edge is interrupted by a bevelled arcuate reaction face located laterally of the axis of rotation. A flat end wall cooperates to in part balance the hydraulic moments created by fluid flow exerted upon the ball element.
U.S. Pat. No. 3,591,129 to Hulsey is directed to a valve for controlling fluid flow employing a ball-shaped closure member having a flow passage comprising an inlet portion circular in cross-section merging into an outlet end portion defined by a laterally extending slot of generally triangular shape. The valve has a tubular housing and flow ports defining a flow way, with a closure chamber for a ball-shaped closure. The ball-shaped closure has an inlet of circular shape and an outlet of generally L-shaped cross-section forming a triangular slot. A flow straightener core is installed to obviate turbulence. The straight slot and slot opening of the ball results in no wall surface of the ball subject to angular impingement by the fluid flow, hence no torsional force will tend to rotate the ball from the desired position.
U.S. Pat. No. 3,689,026 to Self is directed to an eccentric rotary plug valve with the center of the plug seat offset from the shaft axis. The valve structure with an outer housing has a closure element that is a plug or poppet supported by rods on opposite sides of the flow tube. The rods connect two operating shafts and in the closed position, the poppet or plug seats against the ring and seals fluid flow. In the open position, the tapered flow tube provides an unimpeded path through the valve.
U.S. Pat. No. 3,826,281 to Clark is directed to a ball valve with low break-away and operating torque provided by a ball with a porous core. The ball valve with body, seat and trunnions, has a ball with a porous core of sintered metal. This construction with the core providing a complete sphere with no sharp edges, prevents damage to the seal, provides good throttling control and low operating torque.
U.S. Pat. No. 5,018,703 to Goode is directed to a valve design to reduce cavitation and noise comprising a valve body having an inlet, an outlet, passages communicating with a valve chamber, a valve element, movable through the valve chamber adjacent a valve seat, and a flow deflector ring having a central opening which has discontinuous deflector surfaces around a central opening separated by spaced grooves arranged to disrupt flow, and prevent the formation of a vena contracta downstream from the valve seat. Sleeves, having cylindrical walls divide the valve chamber. An array of inlet bores are formed in the sleeve and an array of exit bores are formed in the other sleeve. The inlet bores are inclined relative to the outlet bores to form a tortuous flow path to minimize noise and cavitation as pressure is reduced in the valve chamber.
Thus there is an ongoing need for an innovation in double-block and bleed plug-type valve implementation which provides a counterbalancing torque against the inherent closing torque of plug-type valves in response to flow therethrough so that conventional methods for resisting such closing torque can be minimized or entirely eliminated thereby reducing the cost and complexity of plug-type valves and minimizing the risk of a sudden and inadvertent closure of the valve which could have deleterious effects on the entire system in which the valve is located.